DTC 15

Fig. 002 - Wiring Diagram for Code 15 Coolant Sensor Circuit (Signal Voltage High). VIN J:

CODE 15

COOLANT SENSOR

(SIGNAL VOLTAGE HIGH)

1.8L TURBO "J" SERIES

The Coolant Temperature Sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on CKT 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore the ECM will see high signal voltage.
As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature the voltage will measure about 1 to 1.5 volts at the ECM terminal C10.

Code 15 will set if:
a. Signal voltage indicates a coolant temperature less than -35°C (-30°F) for 4 seconds.
b. Time since engine start is more than 1 minute.

A Code 15 can be caused by:
a. An open coolant sensor
b. Faulty wiring or terminals
c. A faulty ECM

Coolant temperature is one of the inputs used to control:
a. Fuel delivery.
b. Engine Timing (EST)
c. Knock Control (ESC)
d. Idle (IAC)
e. Convertor Clutch (TCC)

Fig. 001 - Chart - Code 15 Coolant Sensor Circuit (Signal Voltage High):

1. If voltage is above 4 volts, the ECM and wiring are OK.
2. If checking resistance at the Coolant sensor is difficult because of the sensor location, disconnect the ECM C-D connector and check resistance between connector terminals C-10 and D-2.